Differential pressure sensors usually have a tappet passing through a housing wall of the sensor to actuate an external switch device. Such a configuration is necessarily open to pressure leaks and yields to inaccurate readings and/or results, especially in high pressure applications such as for example in ventilation ducts.
Known in the art is U.S. Pat. No. 5,024,294 (Van Fossen et al.), which shows a differential pressure transducer having a diaphragm subjected to different pressures from each side. A rod is attached to the diaphragm, the rod supporting a magnet moving inside the transducer's housing as a function of the measured pressure differential. The rod is suspended at one end by a tension spring, the opposite end of the rod being attached to the diaphragm. The displacement of the rod caused by the flexion of the diaphragm is measured by means of a Hall effect sensor mounted in the transducer's housing.
Also known in the art is U.S. Pat. No. 3,967,504 (Akeley), which shows a differential pressure sensor having a spring subjected to compression when the pressure in a high pressure line exceeds the pressure in a low pressure line.
Also known in the art is U.S. Pat. No. 3,831,588 (Rindner), which shows a pressure measuring device producing an electric signal proportional to the pressure. The device is housed in a chamber having a flexible diaphragm to transmit external pressure to the sensor.
Also known in the art is U.S. Pat. No. 5,817,943 (Welles, II et al.), which shows a pressure sensor having a structure for generating a magnetic force to balance forces on opposite sides of a flexible diaphragm centered within a pressure chamber in which a fluid under pressure is introduced on a side of the diaphragm.
Also known in the art is U.S. Pat. No. 5,303,595 (Shoji et al.), which shows a pressure sensor based on a magnetostriction effect.
Also known in the art is U.S. Pat. No. 5,355,714 (Suzuki et al.) which shows a pressure sensor using a pressure responsive magnetic film to vary the inductance of a coil. The diaphragm is arranged to displace depending on a pressure differential, thereby changing the inductance of the coil.
Also known in the art are U.S. Pat. No. 3,575,054 (Glista); U.S. Pat. No. 3,590,638 (Anastasia); U.S. Pat. No. 4,336,567 (Anastasia); U.S. Pat. No. 4,373,385 (Boutteville et al.); U.S. Pat. No. 4,453,412 (Nakane); U.S. Pat. No. 4,475,405 (Corpron et al.); U.S. Pat. No. 4,487,074 (Herden); U.S. Pat. No. 4,671,116 (Glennon et al.); U.S. Pat. No. 4,716,492 (Charboneau et al.); U.S. Pat. No. 4,876,893 (Kato et al.); U.S. Pat. No. 5,068,503 (Sladky); U.S. Pat. No. 5,219,041 (Greve); U.S. Pat. No. 5,315,878 (Birenheide); U.S. Pat. No. 5,437,241 (Rosenberg et al.); U.S. Pat. No. 5,760,310 (Rud, Jr. et al.); U.S. Pat. No. 5,874,680 (Moore); U.S. Pat. No. 5,880,373 (Barton); U.S. Pat. No. 5,889,212 (Guthrie et al.); and U.S. Pat. No. 5,908,990 (Cummings) which all show various types of pressure sensors illustrating the state of the art.